(i) Field of the Invention
The present invention relates to a fuel cell that directly converts chemical energy of a fuel into electrical energy, particularly to an air supply device for a fuel cell that supplies air as an oxidizing gas to the cathode (oxygen pole) side of the fuel cell.
(ii) Description of the Related Art
Fuel cells can be classified into phosphoric acid type, molten carbonate type, solid oxide type, and solid polymer electrolyte type on the basis of an electrolyte to be used. However, in all types of fuel cell, both the surfaces of an electrolyte plate or an electrolyte film are sandwiched between both the electrodes of the cathode (oxygen pole) and the anode (fuel pole). One cell is comprised with a cathode side to which air (O.sub.2) as an oxidizing gas is supplied and an anode side to which hydrogen (H.sub.2) as a fuel gas is supplied, and such several cells are laminated via each separator into a stack.
A turbo charger model shown in FIG. 1, which drives a compressor with an exhaust gas turbine, and a motor drive model shown in FIG. 2 which drives a compressor with a motor, are examples of conventional air supply devices for supplying air to the cathode side of the above fuel cells.
FIG. 1 is one example showing a turbo charger model used as an air supply device for a natural gas reforming molten carbonate fuel cell generator, with a reformer d mounted on the upper flow side of the fuel cell FC, in which both surfaces of electrolyte plate a are sandwiched between the two electrodes cathode b and anode c, in which cells that supply air A as an oxidizing gas to cathode b, and also supply fuel gas FG to the anode side c are laminated and stacked between separators. It is further equipped with a turbo charger e as a device for supplying air to cathode b comprising an exhaust gas turbine f and a compressor g which is driven by the exhaust gas turbine f. A cathode exhaust gas line h is connected to the intake side of the exhaust gas turbine f, and the exhaust gas turbine f is rotated by the cathode exhaust gas CG. An air supply line i connected to the output side of the compressor g is connected to the inlet side of the cathode b, and a branch line j, divided by the air supply line i is connected to the inlet side of the combustion chamber Co of the reformer d. The air A compressed by the compressor g is sent to the combustion chamber Co of the reformer d and to the cathode b. k is the burned exhaust gas line that conducts the burned exhaust gas discharged from the combustion chamber Co of the reformer d to the inlet side of cathode b; Re is the reforming chamber of reformer d; l is the reforming raw materials line that conducts the raw materials to the reforming chamber Re of the reformer d; m is the fuel gas line that conducts the fuel gas FG reformed in the reformer d to the inlet side of the anode c; n is the anode exhaust gas line that conducts the anode exhaust gas AG to the combustion chamber Co of the reformer d after the moisture had been extracted by the gas/water separator o.
FIG. 2, as opposed to the turbo charger model shown in FIG. 1, shows a device in which the compressor g is driven by the motor M. Compressor g is directly driven by motor M, and air A conducted from the inlet side of compressor g is pressurized and supplied to the fuel cell cathode through the output side as in FIG. 1.
In the turbo charger shown in FIG. 1, the exhaust gas turbine f is rotated by cathode exhaust gas discharged from cathode b, drives the compressor g. The relationship of the flow rate Q to the pressure P is as shown in FIG. 3: when the flow rate falls, the pressure also falls. Therefore there is the danger of surging in a low flow rate range, and one must adjust both the flow rate and the pressure.
In the motor driven model shown in FIG. 2, the problem is that the exhaust gas energy discharged from the fuel cell can not effectively be used as motive power for supplying air, and the electricity obtained from the fuel cell is used for driving motor M, and is thus wasted.